Misted Double Glazing
If you have a double glazed sealed unit that has gone misty then there it is likely that there is a fault has developed in the perimeter of the unit and now moisture is getting inside and between the two panes of glass causing a mist.
Heat and temperatures change moisture into liquid and this cannot escape and will only get worse with age.
When sealed units is manufactured it not designed to be taken apart again and a failed unit needs to be replaced completely.
This is not a total disaster as old glass does not have the same energy efficient ratings as new glass so replacing the unit will be a good thing in the long run.